As a technique for a user to be securely authenticated simultaneously by each server when the user receives a service in which a plurality of servers are involved, techniques described in Non-patent literatures 1 to 3 are known (see, for example, Non-patent literatures 1 to 3). The techniques described in Non-patent literatures 1 to 3 are authentication techniques in a secure storage service, in which a user sets a password, and data is dispersed and stored in a plurality of servers by a secure method called secret sharing. If a password inputted at the time of authentication is correct, the user can reconstruct correct data. If the password is wrong, the user fails in reconstruction.